The present invention relates to a camera device for recording an image, and more particularly to a camera device for safeguarding a hazardous area of an automatically operated installation. Moreover, the invention relates to an image sensor for such a device and to a method for recording an image with an image sensor.
WO 01/78411 A1 discloses a protective device for safeguarding a hazardous area, such as the hazardous area of an automatically operated installation. The protective device is based on the idea of recording an image of the hazardous area using a camera, and to be more precise using an image sensor. The recorded image is then subjected to evaluation in order to establish whether an unauthorized object is located in the hazardous area. If this is the case then the protective device initiates a suitable action. By way of example, the protective device brings the monitored installation into a safe state by turning it off or by controlling it into a safe rest position. The protective device of WO 01/78411 A1 therefore fulfills tasks for which, to date, light barriers, light curtains, protective fences and the like typically have been used.
The camera based protective device therefore fulfills safety-critical tasks. It is thus necessary to ensure that the protective device operates in a functional reliable and fail-safe manner to a degree which reliably rules out any risk to people as a result of faults in the operation of the protective device. The novel protective device therefore needs to have a single-fault safety and needs to meet at least the requirements of category 3 of European standard EN 954-1 or comparable safety requirements. Preferably, the requirements of category 4 of EN 954-1 or comparable requirements should be met. This requires regular function tests on the device in the course of operation.
For safeguarding the hazardous area in a reliable and continuous manner, the aforementioned WO 01/78411 A1 proposes to selectively make dynamic an object image recorded by the image sensor. Evaluation of the changes which are thus brought about artificially in the object image allows the functional reliability of the image sensor to be monitored. This allows early detection of what are known as stuck-at faults, for example, where single or a plurality of image cells in the image sensor provide a constant image signal value regardless of the incident light.
However, selectively changing the object image requires components which influence the path of rays in the incident light on the image sensor. This makes the known device rather complex and expensive.
As an alternative, WO 03/067900 A1 proposes a method for checking the functional reliability of an image sensor based on statistical analysis of the image signal values from the image sensor. This involves evaluating the noise response in the image signal values from the image sensor. Changes in the noise response allow conclusions to be drawn about possible faults in the operation of the image sensor.